When searching through our site repo, I find myself frequently excluding the same directories, due to my search results being flooded by maddeningly long ugly lines of CSS, javascript and other pointless crap:
egrep -ri SomeSearchTerm \
--exclude-dir=assets
--exclude-dir=_site \
--exclude-dir=vendor \
./*
I found that I was able to shorten this considerably by excluding multiple directories at the same time:
$ egrep -ri SomeSearchTerm --exclude-dir={assets,_site,vendor} ./*
But I still got tired of typing that over and over, so I thought I’d export it as an environment variable:
$ export EXCLUDE_DIRS="--exclude-dir={assets,_site,vendor}"
To my surprise, it didn’t work, but the reason it didn’t work turned out to be pretty interesting.
This gives me the results I want (excluding search results from the assets, _site and vendor directories):
$ egrep -r SearchTerm --exclude-dir={assets,_site,vendor} ./*
Lo, to my confusion, this does not:
$ export EXCLUDE_DIRS="--exclude-dir={assets,_site,vendor}"
$ egrep -r SearchTerm $EXCLUDE_DIRS ./
Why doesn’t it work?!
Behold:
$ echo --exclude-dir={a,b,c}
--exclude-dir=a --exclude-dir=b --exclude-dir=c
Smart right? The shell performs brace expansion on {a,b,c}. Except it only does this when passed directly, not when it’s stored as an environment variable. Foiled!
eval $() to the rescue
The solution:
$ export EXCLUDE_DIRS="eval $(echo --exclude-dir={assets,_site,vendor,_posts,api})"
$ egrep -r Service $EXCLUDE_DIRS ./*
No more stupid scrolling walls of minified CSS!
There’s more
As pointed out by @Matthieu_xyz, spaces will try to ruin everything:
$ echo --exclude-dir={w,t,f} # yay :)
--exclude-dir=w --exclude-dir=t --exclude-dir=f
$ echo --exclude-dir={w, t, f} # nay :(
--exclude-dir={w, t, f}
So if you really need a space, just escape it:
$ echo --exclude-dir={y,\ a,\ y}
--exclude-dir=a --exclude-dir= b --exclude-dir= c